27 May 2011 SLM-based multipoint vibrometry
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Abstract
Heterodyne interferometry is a very accurate and robust technique for measuring vibrations under industrial conditions. Typically, instruments based on this principle measure on a single point and scanning is employed to obtain operational deflection shapes. For the simultaneous measurement of vibrations (e.g. to detect transients) it is possible to use a fixed arrangement of measurement beams. Dynamic steering of multiple beams, however, is not easy to achieve. In this contribution we present a solution for multipoint vibrometry using a high resolution (HDTV) programmable spatial light modulator as the core element. By using a liquid crystal display (LCD) for displaying a dynamic hologram it is possible to independently control multiple measurement spots in three dimensions with high repeatability and accuracy. Mechanical movements that might introduce noise do not oocur. The main challenge in designing such an LCD-based multipoint vibrometer is to avoid problems due to the unwanted spurious diffraction orders that will be present when using commercially available spatial light modulators for reconstructing holograms. We present a system in which the illuminating as well as the detection is programmable. One half of the high resolution LCD is used for illumination and the other half is responsible for the detection. Different possible methods to avoid spurious diffraction orders are shortly discussed. Emphasis will be laid on a method based on complex multiplexing (using hologram optimization) and a spatial multiplexing method based on Golay arrays. We show the optical design as well as first experimental results for a single detector. Hologram computation is based on a joint optimization of the detection and the illumination hologram using a modified Gerchberg-Saxton algorithm together with combinatorial optimization of the spot/detector mapping.
© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Tobias Haist, Tobias Haist, Alena Tarbeyevskaya, Alena Tarbeyevskaya, Michael Warber, Michael Warber, Wolfgang Osten, Wolfgang Osten, Christian Rembe, Christian Rembe, Mario Ludwig, Mario Ludwig, Wilhelm Stork, Wilhelm Stork, "SLM-based multipoint vibrometry", Proc. SPIE 8082, Optical Measurement Systems for Industrial Inspection VII, 80821V (27 May 2011); doi: 10.1117/12.889337; https://doi.org/10.1117/12.889337
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